Environmental Engineering Reference
In-Depth Information
(b) If the rate of accumulation of CFC-11 and CFC-12 are reduced to
<
0.1% through voluntary limits on CFC production, and that of N
2
O
is reduced to
<
0.1% via stricter automobile emission checks, what
temperature increase can be anticipated in the year 3000?
6.13
2
Free radicals formed in the atmosphere from photochemical species such
as aldehydes can increase the concentration of ozone in urban smog. The
following mechanism is suggested for the effect of formaldehyde upon the
reaction of ozone in the troposphere:
HCHO
h
ν
2HO
2
+
CO
2
;
J
2
=
0.015 min
−
1
−
J
2
k
4
HCHO
+
OH
•
−→
HO
2
+
CO
+
H
2
O;
k
4
=
1.1
×
10
−
11
cm
3
/
molecules
k
5
HO
2
+
NO
−→
NO
2
+
OH
•
;
k
5
=
8.3
×
10
−
12
cm
3
/
molecules
k
6
OH
•
+
NO
2
−→
HNO
3
;
k
6
=
1.1
×
10
−
11
cm
3
/
molecules.
Along with the Chapman mechanisms, the above reactions can be used to
obtain [O
3
] as a function of
t
. Derive expressions for the rate of change in
concentrations [NO], [NO
2
], and [HCHO]. The equations should involve
only terms in [NO
2
] and [HCHO]. From the resulting equations how do
you propose to obtain [O
3
] given the initial conditions [NO]
0
, [NO
2
]
0
,
and [HCHO]
0
.
6.14
2
An enzyme catalysis is carried out in a batch reactor. The enzyme con-
centration is held constant at 0.003 mol/dm
3
. The decomposition of the
pollutant A
−→
E
P was studied separately in the laboratory. It obeys the
Michaelis-Menten kinetics with
K
M
=
5 mM and
V
max
=
10 mM/min,
but at an enzyme concentration of 0.001 mol/dm
3
. How long will it take
in the batch reactor to achieve 90% conversion of A to P?
6.15
2
An organism (
Zooglia ramigera
) is to be used in a CSTR for waste-
water treatment. It obeys Monod kinetics with
μ
max
=
5.5 d
−
1
and
K
s
=
0.03 mg/dm
3
. A total flow rate of 100 mL/min is being envisaged at an
initial pollutant concentration of 100 mg/dm
3
.
C
X
=
10 mg/L: (a) If the
desired yield factor is 0.5, what reactor volume is required? (b) Design a
CSTR in series with the first one that can reduce the pollutant concentra-
tion to 0.1 mg/dm
3
. (c) If the second reactor is a PFR, what size reactor
will be required in part (b)? (d) Which combination do you recommend
and why?
6.16
2
Asolutioncontainingadenitrifyingbacteria
Micrococcusdenitrificans
ata
concentration of 1
10
−
6
kg/dm
3
is introduced into a semibatch reactor
where the growth rate is given by
r
=
k(
[
×
]
)
, where
[O
2
] is the oxygen concentration (mol/dm
3
). An excess of substrate [S]
was used. If after3hofoperation, the concentration of the bacteria is
3
×
10
−
5
kg/dm
3
, what is the specific growth rate of the bacteria?
6.17
2
The rate of growth of
Escherichia coli
obeys Monod kinetics with
μ
max
=
0.9 h
−
1
and
K
s
=
0.7 kg/m
3
. A CSTR is used to grow the bac-
teria at 1 kg/m
3
with inlet substrate pollutant feed rate of 1 m
3
/h and
X
][
O
2
][
S
]
/K
s
+[
S
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